Polypropylene and polypropylene-based materials are commonly employed in structural applications in automobiles. Physical properties that are important in selecting and engineering such materials include stiffness, toughness, dimensional stability, heat distortion temperature, and surface smoothness.
Presently, there are no polypropylene-based materials available that can deliver good performance in fulfilling most or all of the physical properties simultaneously in meeting the needs for structural automotive applications.
One means of addressing the performance needs of polypropylene-based materials in structural automotive applications is to introduce elastomers or talc into the materials to enhance toughness and improve surface finish and paintability. However, introduction of elastomers may diminish heat distortion temperature resistance and dimensional stability.
Another means of addressing the performance needs of polypropylene-based materials in structural automotive applications is to introduce fibers, such as glass fibers, into the materials so as to form a composite. Introduction of high levels, e.g., ≧30 wt %, of such fibers enhances stiffness, dimensional stability and heat distortion temperature resistance of polypropylene-based materials. However, polypropylene-based materials having high levels of fibers, particularly those having diameters of 0.1 mm or more or that are long, are very difficult to process and frequently result in non-uniform fiber concentration. Additionally, polypropylene-based materials having high levels of fibers can be brittle and have a poor surface finish, which prevents them from being used as outside panels. The presence of long glass fibers can also prevents the addition of elastomers into these materials for toughness enhancement.
Another means of addressing the performance needs of polypropylene-based materials in structural automotive applications is to use multi-layer laminates. One layer provides stiffness, dimensional stability, and heat distortion temperature performance while another surface layer of different composition provides surface smoothness, paintability, and impact toughness. However, the use of multilayer laminates adds additional cost due to more complex manufacturing. It would be very desirable to have a polypropylene-based material that would satisfy all performance requirements such it could be used in a single layer.